DE69637079T2 - HOCHGESCHWINDIGKEITSCHROMATOGRAPHIE - Google Patents

Description

Background of the invention

The Invention is for high speed gas chromatography for detection directed by different compounds.

Gas chromatography is used in the U.S. Patent Nos. 5,092,155 ; 5,092,157 ; 5,098,451 ; 5,099,743 ; 5,108,705 ; 5,268,302 ; 5,300,758 ; and 5,310,682 described.

The U.S. Patent No. 3,053,077 discloses a gas chromatograph having a gas chromatographic column and a thermal conductivity detector positioned in a constant temperature air bath.

The U.S. Patent No. 3,139,745 discloses a gas chromatograph having a coiled gas chromatographic column and means for heating the column, comprising a ring heater.

The U.S. Patent No. 5,005,399 discloses a portable gas chromatographic assembly having a gas chromatographic column coated with an electrically conductive film.

The U.S. Patent No. 4,181,613 discloses a furnace for a chromatograph in which inlet and outlet ports are both disposed on opposite sides of a fan from the columns and in such a manner that the ambient air entering through the inlet port communicates with the hot air from the furnace mingled before she reaches the columns.

Summary of the invention

The The invention provides a high speed flash gas chromatography system which provides results in one or two minutes, which one or two hours of processing by conventional gas chromatography systems would require. The system closes a heated isothermal section and a gas chromatography column outside is located from the isothermal area. The system also closes a detector and a flux path between the detector and the gas chromatography column one. At least a portion of the flow path is in the isothermal Positioned area.

embodiments of the invention can be one or more of the following features. The system can be a housing outside the include isothermal area, with the gas chromatography column in the case positioned. The housing can be configured to control the gas chromatography column of the heat sources outside of the housing to isolate. For this purpose, the housing may have an insulating wall between the housing and the isothermal region.

The gas chromatography column includes a conductive metal sleeve and the system may include a circuit for Respectively an electric current to the conductive metal sleeve to Heating the column. To the amount of heat loss from the sleeve to the housing To reduce, the interior of the case is designed to be there has a low thermal mass. For example, the interior of the housing a thin one Layer of metal, which on a thick layer of a thermal insulation rests. This arrangement also reduces the amount of heat which through the interior of the case while consecutive heating / cooling cycles retained becomes.

In addition to the conductive metal sleeve can the gas chromatography column include a layer of electrically insulating material which the conductive metal sleeve surrounds. The material can also provide thermal insulation. For example, the metal sleeve be surrounded by a layer of glass fibers. The gas chromatography column can for reasons the compactness be coiled.

The casing can also be a fan lock in to circulate of air in the enclosure to a homogeneous heat distribution inside the case provided. This air circulation prevents or reduces the occurrence of a so-called chimney effect, which can occur when air heated by lower spirals of air Pillar, ascends and heats the upper filaments of the column.

The casing may also include an inlet which is configured to act in an open position, which flows through the housing allows the inlet, or a closed position, which a flow into the housing prevented by the inlet. A control mechanism, such as flaps, can be attached to the inlet and be operable to the To switch the inlet between the open and closed positions. A processor configured to control the system can be used with be connected to the control mechanism and configured to the control mechanism to cause the inlet to be placed in the open position, around the gas chromatography column to cool.

The system may also include a holder configured to maintain the column in the coiled configuration. For example, the holder can have four side rails and one Include a pair of rings, wherein the side rails are connected to the rings. Each side rail may include grooves on a surface of the side rail which is inside the holder, each groove being sized to receive a coil of the column.

Heat sinks can on be attached to each end of the gas chromatography column. When the isothermal Area is an isothermal chamber, the system can also be a holder lock in, positioned in an outer wall the isothermal chamber. A heat sink, attached at one end of the gas chromatography column may be inserted in the holder. The system may also include a second holder positioned in the outer wall the isothermal chamber, and a heat sink attached at the other end of the gas chromatography column, can in the second holder be inserted.

The Heat sinks can be electric be conductive and attached to the ends of the metal sleeve. The brackets can be configured to provide an electrical current to heat the column through to provide the attachment of the brackets to the heat sinks.

Other Features and advantages of the invention will become apparent from the following detailed Description, including of the drawings, and from the claims.

Brief description of the drawings

1 Figure 12 is a block diagram of a high speed flash gas chromatography system.

2 and 3 are views from above and from the side of a gas chromatography column of the system 1 ,

4 FIG. 12 is a sectional view taken along section 4-4 of FIG 2 ,

5 is a sectional view taken along section 5-5 of 4 ,

6 - 8th are views of a device of the system 1 ,

9 FIG. 11 is an end view showing an orientation of a cold spot of the system of FIG 1 shows.

10A - 10C Figure 12 are schematic views of component configurations in a BLITZ-GC system.

11A - 11D Figure 12 are schematic views of component configurations in a BLITZ-GC system.

12 - 14 Figure 12 are schematic views of component configurations in BLITZ-GC systems.

15 Figure 11 is a general block diagram of a high speed gas chromatography system.

16A and 16B Figure 4 is a block diagram illustrating the interconnections achieved by a six-port two-position valve.

17 is a graph of a temperature versus time.

18 Figure 11 is a block diagram of a system for controlling the temperature of a gas chromatography column.

19 is a flowchart of a method implemented by the system of 18 ,

20 is a timing diagram for the system 18 ,

21 is a graph of a relationship between the resistance ratios and the power duration.

22 FIG. 12 is a cross-sectional view of a gas chromatographic column with a damping control and a device for cooling the column. FIG.

23 FIG. 12 is a cross-sectional view taken along section 23-23 of FIG 22 ,

24 Figure 11 is a schematic view of a vertically oriented gas chromatographic column which may be subjected to thermal gradients.

25 Figure 11 is a schematic view of a vertically oriented gas chromatographic column having a structure to reduce thermal gradients.

26 Figure 12 is a cross-sectional view of a vertically oriented gas chromatographic column with a fan or blower to minimize thermal gradients.

27A - 27F Figures are diagrams of gas chromatography columns having a structure for introducing thermal gradients along the length of the column.

28 is a cross-sectional view of one Sample extraction module.

Description of the preferred embodiments

With reference to 1 includes a high speed flash gas chromatography system 100 a coiled gas chromatography tube 105 a, located in a column housing 110 , Other components of the system 100 are in a valve oven 115 localized.

Also with reference to the 2 and 3 becomes the tube 105 in the coiled configuration held by a lightweight holder 118 which is in the column housing 110 is positioned. To the heat loss from the tube 105 minimize is the holder 118 designed so that he has minimal contact with the tube 105 having. For this purpose, the holder closes 118 four side rails 120 one with a pair of rings 125 are connected. The side rails 120 are around the tube 105 positioned and closing grooves 130 one, each of which is sized, a coil 135 to record the tube. The distance between the grooves 130 Controls or controls the vertical distance between the coils 135 , The side rails are made of Micra or an electrically and thermally insulating material.

The Rings 125 , which are made of metal, are smaller in diameter than the helices 135 and they are at the top and bottom of the holder 118 positioned. brackets 140 on the rings are on the side rails by screws 145 appropriate. The shape of the rings 125 and the orientation of the side rails 120 with respect to maintaining the coiled configuration of the tube 105 ,

With reference to the 4 and 5 closes the tube 105 a gas chromatography column 150 comprising a layer of polymer 155 coating an inner surface of a glass or quartz fused silica tube 160 having. The pillar 150 is inside a sleeve 165 isolated from stainless steel. The sleeve 165 can be rapidly heated by applying an electric current, and it is within an electrically insulating, interwoven glass sleeve 170 localized. The glass sleeve 170 allows the grooves 130 ( 2 ), so close to each other that the coils 135 ( 2 ) can touch each other without generating an electrical short circuit. If the grooves 130 spaced far enough away that the filaments could not touch, would the glass sleeve 170 not necessary.

To insert the column 150 in the sleeve 165 to allow, is the outer diameter of the column 150 smaller than the inner diameter of the sleeve 165 , The difference between the two diameters must be large enough to allow insertion of the column 150 in the sleeve 165 but it must be small enough to allow rapid heat transfer from the sleeve 165 to the pillar 150 to allow. For example, the column points 150 in one embodiment, an outer diameter of 0.5 millimeters, while the sleeve 165 has an inner diameter of 0.55 millimeters.

Referring again to the 2 and 3 are heat sinks 175 to each end of the sleeve 165 melted. The heat sinks 175 prevent the temperature of the ends of the sleeve 165 Remember to exceed a desired temperature when applying an electrical current to the sleeve 165 is applied to the sleeve 165 and the pillar 150 to heat. In extreme cases, this prevents the destruction of the sections of the column 150 at the ends of the sleeve 165 , The heat sinks 175 can be made of brass or other suitable conductive materials.

With reference to the 6 - 8th is every heat sink 175 configured to fit in a holder 200 to be inserted. The heat sinks 175 Provide structural rigidity, which helps in placing the heatsink within the mounts 200 helpful. This simplifies the process of replacing the tube when a column 150 which is a different polymer 155 has, is desired or if a column 150 is worn or damaged.

As in the 1 and 6 shown is every bracket 200 on a wall 205 between the case 110 and the valve furnace 115 appropriate. The bracket closes a first section 210 which is inside the valve furnace 115 is positioned, and a second section 215 , which extends through the wall 205 extends. The first paragraph 210 is on the wall 205 through a pair of threaded studs 220 attached.

Electric lines 225 are at the first section 210 through a second pair of threaded studs 230 attached. A first electrical line of each holder 200 is used to form a circuit through which an electrical current to the sleeve 165 ( 5 ) is applied to the sleeve and the column 150 to heat. A second electrical lead of the first holder is used to form a circuit which determines the electrical resistance of the sleeve 165 measures. Because the resistance of the sleeve 165 varies with temperature, the measurement of the resistance can be used to measure the temperature of the sleeve and the column.

Alternative techniques for measuring the temperature of the tube include winding a wire through the sleeve 165 and along the pillar 150 and measuring the resistance of the wire as a measure of the temperature. This approach allows the sleeve 165 may be made of a material having a resistance that varies little with temperature. Use of such a material provides greater control of the temperature profile over which the sleeve rests 165 can be heated. For example, a linear temperature rise can be achieved much more easily if the resistance varies little with temperature than if the resistance varies greatly with temperature. A temperature sensor can also be made by coating the column 150 with a layer of metal and then measuring the resistance of the metal layer. A metal coating on the column 150 Can also be used to the metal sleeve 165 to replace. Similarly, the sleeve could 165 be eliminated by using a column 150 which is a tube 160 made of a metal instead of fused silica. In other alternative approaches, a thermocouple may be inside the sleeve 165 or inside the case 110 be placed.

ribs 235 on the exterior of the first section 210 provide a heat transfer between the attachment 200 and the interior of the valve furnace 115 to the attachment 200 at the temperature of the furnace 115 to keep. As an additional mechanism for maintaining the fixture at the temperature of the furnace, a heater (not shown) could be included within the fixture. A compression mount 240 is used to heat sink 175 and the sleeve 165 on the bracket 200 to fix. As in 1 shown, the ends of the column extend 150 through the heatsink 175 and the brackets 200 in the valve oven 115 , The ends of the column are with a valve 250 connected.

Referring again to 1 allows the use of a separate columnar housing 110 a high speed temperature programming of the tube 105 regardless of the temperature of the valve furnace 115 , As noted above, the tube is electrically heated by applying an electrical current to the sleeve 165 through the heatsink 175 and their connections to the brackets 200 , It has been found that a power supply (not shown) capable of delivering up to 96 volts at 12 amps provides sufficient power to the tube 105 to heat to desired temperatures.

A heat loss from the tube to the air in the housing 110 is reduced by the presence of the glass sleeve 170 which over the sleeve 165 lies, and by dimensioning the housing 110 to fit closely to the dimensions of the coiled tube 105 zusammenzuliegen. Heat loss of air to the housing is reduced by reducing the mass of the housing 110 , For this purpose, the interior of the housing encloses a thin layer of a metal 252 one which over a thick layer of insulation 254 lies. The mass within the housing is also reduced by reducing the mass of the holder 118 ,

The column housing 110 Also sees a homogeneous heat distribution during heating of the tube 105 in front. Due to limitations in the dimensions of the system 100 is the tube 105 vertically oriented, with successive spirals stacked over each other. To avoid the occurrence of a chimney effect (ie, excessive heating of the upper coils due to the rising heat) and to ensure homogeneous heat distribution, a small fan rolls 255 Air inside the column housing 110 around. The effect of the chimney effect is also diminished by having samples in the tube 105 enter at the lower helix and from the tube 105 emerge at the upper spiral. The chimney effect can also be prevented by orienting the tube 105 placed horizontally, with successive spirals along each of their sides.

Around the tube 105 To cool, dome or vents are 260 in the bottom of the case 110 opened to the inside of the housing an area 262 from positive pressure, generated by a blower 265 which is below the housing 110 is positioned. When the flaps are opened, air comes out of the area 262 in the case 110 and exits the housing through slots 270 in the top of the case 110 out. The slots 270 are small enough that no considerable heat due to the air flow through the slots 270 gets lost when the flaps 260 are closed. Venting can be achieved by using the fan 255 instead of the blower 265 used. However, the resulting increase in the mass of the fan would be with the aim of reducing the mass within the housing 110 to be in conflict.

The housing 110 also closes a door 275 one. The door can be opened to access the interior of the case 110 and to the tube 105 provided.

In general, the temperature of the tube 105 lower than the temperature of the furnace 115 , which is controllable between 50 ° C and 400 ° C. The temperature of the furnace 115 can be maintained at 300 ° C to ensure that samples introduced into the system will be in a vaporized state when not in the tube 105 are located. Whether the samples ver be steamed when they are in the tube 105 is dependent on the temperature to which the tube 105 is heated.

The system 100 closes an injector 300 a, which allows the introduction of a sample into the system. The injector may be a standard gas chromatography gap / non-gap injector. An inner surface of the injector is heated to a temperature sufficient to vaporize the sample. A tube 305 connects the injector to the valve 250 , When the valve 250 For sample introduction, the vaporized sample is carried by the injector into the valve.

With reference to the 1 and 9 is a cold point 310 (also referred to as a vapor concentrator) with the valve 250 through a pair of tubes 315 connected. In essence, the cold spot 310 a short gas chromatography column 320 , which can be cooled rapidly to concentrate vapors, and which can be heated quickly to release the concentrated vapors. Like the tube 105 is the pillar 320 from a metal sleeve 325 surrounded, which can be heated by applying an electric current.

The pillar 320 is inside a slot 330 in a block 335 of thermally conductive material (eg aluminum), which itself is embedded in a back wall 340 of the furnace 115 , A layer of silicone 345 is in the slot 330 extruded to surround the sleeve and provide electrical insulation as well as some thermal insulation. The block 335 Provides a large thermal mass and holds the column 320 at a constant temperature when no power is applied to the sleeve 325 is created.

The block 335 is kept at a low temperature by a pair of Peltier coolers 350 , heatsink 355 on the outside of the back of the furnace release heat from the Peltier coolers. The Peltier coolers are capable of blocking the block 335 to cool to a temperature which is about 25 ° C less than the room temperature and which is substantially independent of the temperature of the furnace 115 , Thus, if the room temperature 30 ° C, the temperature of the block should be kept at 5 ° C. This is true even when the temperature of the furnace 115 400 ° C is.

Vapors entering the cold spot become attached to the polymer coating of the interior of the column 320 bound. Less volatile compounds are bound immediately upon entry of the cold point, while more volatile compounds continue to bind along the interior of the column 320 wander before they are tied.

Connections are from the column 320 solved by applying an electric current to the sleeve 325 to the sleeve 325 and the pillar 320 to heat. Before heating the column 320 can the valve 250 be adjusted to the flow through the column 320 turning around. This increases the likelihood that compounds of varying volatility will leave the column 320 will leave at or near the same time. In particular, more volatile compounds which are dissolved earlier by the polymer will have to travel a longer distance before leaving the column 320 leave because they will have moved further into the column before they are tied. In contrast, less volatile compounds which are later dissolved by the polymer will have to travel a shorter distance before they reach the column 320 leave as they will have traveled a shorter distance into the column before they are tied.

The system 100 also includes a gas chromatography detector 360 one. The detector 360 is a standard flame ionization detector, except that electronics 365 assigned to the detector operate much faster to provide a higher sampling rate than that offered by electronics associated with standard detectors. Typically, about ten data samples are needed to define a peak. Because the system 100 At least one order of magnitude faster than conventional gas chromatography systems may require that the sampling rate be an order of magnitude higher than the sampling rates associated with data systems for standard gas chromatography systems. Other suitable detectors include photoionization detectors, electron capture detectors, mass spectrometers, pulsionization detectors and mass selection detectors.

The valve furnace 115 is similar to a conventional gas chromatography furnace. However, unlike conventional gas chromatography furnaces which require providing a controlled temperature profile for the gas chromatography column, the valve furnace requires 115 it only to maintain a single temperature. Accordingly, the valve furnace 115 easier and less expensive than conventional gas chromatography furnaces.

The system 100 is through a processor 370 controlled. The processor 370 controls the temperature of the gas chromatography tube 105 and the temperature of the cold point 310 , In particular, the processor measures 370 the temperature of the tube 105 and controls the electrical current leading to the sleeve 165 through the heatsink 175 for heating the tube 105 is supplied. The processor 370 also controls the flaps 260 to the tube 105 to cool, if appropriate. The processor 370 controls the cold point 310 in a similar way.

The processor 370 also controls the flow through the system 100 by controlling the valve 250 , For simplicity of illustration, the valve 250 shown and discussed as a single valve. In actuality, the valve may include a plurality of valves, and may include additional connections, for example, to a supply of a carrier gas (not shown) and a vent (not shown). The important point is that the valve (or valves) must be controllable by the processor to control flow through the system in a desired manner. For example, the processor may initially configure the valve to receive samples from the injector 300 through the cold point 310 flow before venting to the atmosphere. When a sufficient amount of sample through the cold spot 310 is collected, the processor reconfigures the valve so that a flow through the cold point 310 is turned over and the samples emerging from the cold spot into the gas chromatography tube 105 enter.

For simplicity of description, the system was 100 described above as a single gas chromatography tube 105 and a single cold spot 310 including. However, actual implementations of the system may include additional gas chromatography tubes and cold spots as well as multiple injectors and multiple detectors. For example, the BLITZ Gas Chromatography System ("the BLITZ GC"), available from Thermedics Detection, Inc. of Chelmsford, Massachusetts (the assignee of this invention), includes two gas chromatography columns and up to four cold spots independently heat and cool, and provide heating rates of 1 ° C per second to 100 ° C per second The cold spots can be temperature programmed to independently heat and cool, and provide heating rates as fast as 6000 ° C per second The BLITZ-GC provides resolution of peak widths of less than 100 milliseconds, and can perform complex chromatograms in less than a hundred seconds.

conventional Gas Chromatography conditions serve as a guide to the best pillars and To select operating parameters. Once a device for the application is sealed, presses on Processor the BLITZ GC. Temperature profiles and valve timing sequences are controlled using a keyboard. GC conditions can evaluated and tested quickly.

In the FLASH GC is the sample introduction step of the gas chromatography columns which allows both operations to be optimized for maximum performance are. Samples are introduced to a cold spot which concentrates the sample and focused on an introduction the sample into the gas chromatography column. As noted above, is the cold spot a short length either fused silica or metal tubing, very similar to conventional ones Gaschromatographieverrohrung. The piping, which is about 10 cm long, has a special metal sleeve on it, allowing it to move quickly and cooled reproducibly and can be heated under the control of a processor.

The Temperature of the cold point is over his length kept constant. The rate of temperature rise (or drop) over its entire length becomes controlled by the operator using the processor. Nearly each heating profile (including an increase, a flat attitude and a decrease in temperature) can be selected. The processor updates and monitors the temperature profile every millisecond. Heating rates are very fast, of 4 ° C per second up to 6000 ° C per second.

Isolation of the sample introduction operation from the gas chromatographic column allows for simultaneous and independent optimization of the sample inlet stage and the gas chromatography columns without crosstalk between the two stages. The 10A - 10C show two cold spots arranged in series and isolated from the gas chromatographic column. The first cold spot is used to collect the sample, and the second cold spot is used to tightly focus the sample prior to analysis. 10A shows the system in a configuration suitable for collecting a sample. As shown, the carrier gas and sample pass from the injector through the valve and the first cold spot before being vented to the atmosphere. At the same time, a carrier gas passes through the valve, the second cold spot, the column and the detector to purify these components of the system. As in 10B 2, in a sample focusing configuration, the first cold spot is heated and the valve is adjusted to collect the sample desorbed from the first cold spot from the second cold spot. Finally, as in 10C in a sample analysis configuration, the second cold spot is heated so that the sample desorbed from the second cold spot enters the column. The in the 10A - 10C For example, the illustrated arrangement may be used to concentrate and pool samples from multiple injections at the second cold spot and then to analyze the combined samples to thereby increase the amount of sample introduced to the gas chromatography column.

The cold spots focus the sample as a narrow band for very rapid and reproducible introduction to the gas chromatographic column. For the smallest peak widths, the cold spot is desorbed in the reverse direction. A schematic current for this application is in the 11A - 11D shown. As shown, the system includes two cold spots, two valves and two gas chromatography columns arranged in parallel. In 11A the system is configured for sample introduction. Less volatile compounds are bound by the first cold spot, which is cooled to 50 ° C, whereas more volatile compounds are bound to the second cold spot, which is cooled to 10 ° C. A carrier gas is passed through the gas chromatography columns and their associated detectors to purify these components. In 11B the second cold spot is heated and the first valve is set to allow analysis of desorbed materials from the second cold spot through the gas chromatographic column and its associated detector. In 11C the first cold spot is heated, the second cold spot is cooled, the first valve is rotated to allow intake by the second cold spot of desorbed materials from the first cold spot, and the second valve is rotated to allow subsequent transfer from the second cold spot to allow for the second gas chromatography column. Ultimately, in 11D the second cold spot is heated and the first valve is adjusted to allow analysis of desorbed materials from the second cold spot by the second gas chromatography column and its associated detector. Typical peak widths, depending on the operation, can range from 100-200 milliseconds. The operator selects the exact time in the process of rapidly introducing the sample to the gas chromatography column. Since the compound of interest in the hot zone of the gas chromatographic column is typically only for a few seconds, thermally labile compounds, which are not normally suitable for gas chromatography, can often be analyzed.

As in 12 As shown, the two gas chromatography columns can be arranged and operated in series. Alternatively, as in 13 shown with two injectors, the BLITZ-GC can be configured to perform two completely different analyzes simultaneously, thus serving as two separate, very fast gas chromatography systems.

Each gas chromatographic column is covered with a metal which allows it to be heated rapidly and reproducibly at heating rates up to 100 ° C per second. In addition to the rapid heating, rapid cooling of the column can be used as part of the temperature profile. For example, chromatography on the first column can be temporarily frozen by rapidly cooling the column while the second column completes its high speed chromatogram. The first column may then be heated with a square wave profile to regain its previous temperature, and then allowed to continue with its temperature profile. In addition, different portions of the first column may be grouped together at one or more cold spots, which in turn may then be analyzed by the second column. The block flow diagram for this arrangement is in 14 shown.

One additional Advantage of the very fast heating rates is that the gas chromatography column at the end of each chromatogram can be baked by heating the gas chromatography column high up to the maximum temperature of the column materials. The gas chromatography column is doing so before the next Analysis cleaned. This feature allows tens of thousands of analyzes per gas chromatography column without deterioration.

15 provides a general block diagram of a high speed gas chromatography system 500 similar to the system 100 which is discussed above. Major components of the system include a carrier gas supply 505 , a sample extractor or extractor 510 (which the injector 300 of the system 100 corresponds), a steam concentrator 515 (which the cold point 310 of the system 100 corresponds), a gas chromatography column 520 and a detector 525 ,

The carrier gas supply 505 generates a heated carrier gas and carries the carrier gas to the sample extractor 510 to. Suitable carrier gases include air, hydrogen, helium, and other gases which are introduced by the system 500 used are inert.

The sample extractor 510 provides the sample to be analyzed. The sample may be a fluid sample or a gas sample. Alternatively, the sample extractor may contain materials to be analyzed, such as, for example, granules (eg, cereal grains) or other granular materials contaminated with substances to be detected (eg, pesticides). As the heated carrier gas passes through the materials to be analyzed, the carrier gas extracts a vapor sample from the materials and delivers the vapor sample from the sample extractor 510 out.

The sample extractor 510 is shown by way of example. The vapor sample and the carrier gas supplied to the system may be replaced by others suitable agents are prepared. For example, the carrier gas could be passed over a metal support covered with a gas chromatography polymer material on which organic compounds have previously been trapped.

On a stimulating the sample extractor 510 The vapor sample and the carrier gas pass through a valve 530 before putting in the steam concentrator 515 enter. The steam concentrator 515 may be identical or similar to the cold point 310 , discussed above. In addition, the steam concentrator 515 be of the form as they are in U.S. Patent No. 5,098,451 is shown. In some systems, the steam concentrator could 515 be removed or replaced by a plurality of vapor concentrators, which are arranged sequentially or in parallel.

In general, the steam concentrator 515 be formed of a short gas chromatography column, which is configured to be heated or cooled quickly. For example, the vapor concentrator may be formed of a glass tube lined with a gas chromatography material capable of absorbing the substances of interest from the carrier gas stream and positioned in a length of small diameter metal tubing (eg, stainless steel needle bearing tubing).

When the carrier gas and the vapor sample through the concentrator 515 pass through, the vapor sample is absorbed by and concentrated in the chroma tographiematerial lining the concentrator. The carrier gas and any remaining vapor sample will be excited by the concentrator 515 through a valve 535 dissipated to the atmosphere.

As the vapor sample is concentrated in the concentrator, a carrier gas is released from the carrier gas supply 505 to the gas chromatography column 520 through a valve 540 fed. The carrier gas cleans the column 520 and returns the column to ambient temperature. On a stimulation of the column 520 towards the carrier gas is through a valve 545 dissipated to the atmosphere.

The gas chromatography column 520 may be identical or similar to the tube 105 of the system 100 be. Another suitable gas chromatography column is in U.S. Patent No. 5,098,451 described. In general, the gas chromatography column 520 similar to the concentrator 515 be formed as described above, but it may be of a longer length (eg 1 to 18 meters long). For compactness, the column can be coiled as a compact helix. Coiling the column also helps to prevent column leakage due to thermal expansion.

When a sufficient amount of steam sample through the concentrator 515 is adsorbed, the concentrator is heated rapidly by applying an electric current to the metal tube. In particular, the concentrator is rapidly heated to a temperature sufficient to desorb the substances previously adsorbed by the concentrator so that these substances are then ejected into the carrier gas stream as a concentrated sample. The ejected sample may form a short burst or plug that lasts for 25 to 100 milliseconds. The temperature to which the concentrator 515 is not sufficient to disassemble the materials of interest in the sample.

When the concentrator 515 is heated, the valves are 535 and 540 reset so that the carrier gas and desorbed material from the concentrator pass through the valves and into the gas chromatography column 520 enter. In the gas chromatography column 520 For example, the components of the desorbed materials are time resolved so that the different components leave the gas chromatography column at different times.

After passing through the gas chromatographic column, the carrier gas stream containing the spaced components passes through the valve 545 through and enters the detector 525 one. Like the detector 360 can the detector 525 a flame ionization detector, a thermal conductivity detector or other detector commonly used in gas chromatography. The detector 525 provides an indication or designation of vapor concentrations at different times. Since the time required for different materials to pass through the gas chromatographic column is known, the relative concentration of a particular material in the sample can be determined by examining the signal generated by the detector at a time corresponding to that material.

In some cases, the detector can 525 a pyrolysis sampler which breaks certain components of the sample vapor into compounds which are more easily detectable by the detector while leaving other components untouched. For example, if the system is configured to detect nitrogen compounds, the detector may include a pyrolysis sampler configured to break nitrogen compounds into nitrogen oxides.

The valves 530 . 535 and 540 can together be operated to operate simultaneously, or they may be formed of a single high-speed two-way valve 550 with 6 connections, as in the 16A and 16B shown. The valve 550 is a rotary switch valve which has two positions (A and B) between which the valve can be changed in as little as 50 to 150 milliseconds.

The valve 550 has six terminals, which are designated by numbers 1 to 6. The outlet of the sample extractor 510 is connected to port 1. The steam concentrator 515 is connected between the terminals 2 and 5. The gas chromatography column 520 is connected to port 3. The carrier gas supply 505 is connected to port 4 and the connection to port 6 is vented to the atmosphere.

In position A, as in 16A shown connects the valve 550 the terminals 1 and 2, the terminals 3 and 4 and the terminals 5 and 6 with each other. With this arrangement, the output of the sample extractor 510 (through ports 1 and 2) to one end of the concentrator 515 connected, and the other end of the concentrator 515 is vented to the atmosphere (through ports 5 and 6). Thus, vapor samples become in the concentrator 515 concentrated when the valve is in position A. At the same time is the gas chromatography column 520 (through ports 3 and 4) to the source of carrier gas 505 connected so that the carrier gas the column 520 cleans.

After a sufficient sample through the concentrator 515 has been collected, which can occur in as little as 1 to 10 seconds, the valve will 550 to position B, shown in FIG 16B , switched. In this position the valve connects 550 the terminals 1 and 6, the terminals 2 and 3 and the terminals 4 and 5 with each other. Accordingly, the carrier gas and the vapor samples from the sample extractor 510 vented to the atmosphere through ports 1 and 6. Also, the carrier gas enters from the carrier gas supply 505 in the steam concentrator 515 on (through ports 4 and 5) and, upon exiting the concentrator, enters the gas chromatography column 520 (through ports 2 and 3) and the detector 525 one. When the valve 550 is in position B, the direction of the flow through the concentrator 515 reversed with respect to the direction of the flow when the valve is in position A. If desired, a second concentrator may be placed between port 3 and the gas chromatographic column 520 be interposed.

As soon as the valve 550 Switched from position A to position B, the concentrator 515 heated up quickly under the control of a computer. As a result, vapor samples, previously through the lining of the concentrator 515 adsorbed and desorbed and to the gas chromatography column 520 transferred in a tight plug with good spatial coherence.

Vapors released from the gas chromatographic column 520 leak, become the detector 525 fed. The output of the detector 525 may be supplied to a host computer (not shown) for graphically displaying the components of the sample analyzed by the detector.

The valves 530 . 535 . 540 and 545 (or the valve 550 with 6 connections) can be used together with the steam concentrator 515 and the detector 525 be housed in a grounded, insulated enclosure or oven. The purpose of the oven is to keep the valves, the tubing that connects them, and the detector hot enough so that the vapors from the sample are effectively transported and do not adhere to surfaces of the system components. The suitable temperature of the furnace selected to provide efficient transport without disruption of the compounds of interest varies with the material to be analyzed and is typically in the range of 150-300 ° C.

Various improvements in the operation and structure of very high speed gas chromatography systems, such as the systems incorporated in the 1 and 15 and similar systems having multiple gas chromatography columns and vapor concentrators are discussed below. Such improvements, in particular the heating, cooling and construction of the gas chromatography columns and concentrators, provide improved control of the gas chromatographic analyzes. As a result, the improvements allow rapid and accurate analysis of the contents of the successive vapor samples. In the following discussion, reference will also be made to the heating and cooling of gas chromatography columns simultaneously for the gas chromatography columns used in the sample analysis and the gas chromatography columns included in the vapor concentrators.

The gas chromatography column

In general, a gas chromatography column that is heated rapidly should be continuous, and should not include any connections, such as tube-to-tube or tube-to-valve connections. A compound tends to have an increased mass which heats non-uniformly during rapid, dynamic heating. This non-uniform heating can lead to gas leaks at the connection (which is difficult to and in turn can lead to inaccurate chromatography. Leaks can be completely avoided by dynamically heating a single tube with no connections and, as above with respect to 1 discussing arranging all connectors and connections in an isothermal furnace.

As noted above, the metal sleeve, which the gas chromatography column surrounds when using the gas chromatographic column. To this To reach, the inside of the metal tube must be deactivated, passivated or otherwise coated as intended for J & W ProSteel or Alltech SilcoSteel piping or for a glass-lined tube. Once the inner surface the metal tube has been treated correctly, becomes a stationary gas chromatography phase directly on the inner surface appropriate. Electrical connections can be made directly with the metal tube like this be that tube can be heated by resistance. The use of a metal tube as the Pillar offers a more direct heat transfer to the stationary one Phase, since disturbing Layers of air and other materials are removed.

One Problem with using a metal tube like about a ProSteel tube or a SilcoSteel tube related, is that the resistance of the tube is very low, causing difficulty in measuring changes can result in resistance due to temperature changes. To this problem can fix the outside the metal tube with a thin layer an electrical insulation (e.g., polyamide) which is a thin one Layer of metal (e.g., nickel) is coated. The thin outer layer of the metal would to a relatively big change in the resistance with the temperature, and the resistance of the thin outer layer could as a measure of the temperature of the internal, resistively heated metal tube to be monitored. The usage a separate metal layer for measuring the resistance will also simplify the circuit which is used to control the heating of the metal tube is used.

One alternative approach of using a metal shell to heat the gas chromatographic column, which is not part of the present invention is to use the gas chromatographic column with Wrap around a wire and heat the wire. This can be realized in different ways. First, the Wire are wound directly onto the gas chromatography column. Second, you can the wire around a thin-walled, non-conductive sleeve be wrapped, in which the column is positioned, what a would allow rapid replacement of the gas chromatographic column. When third, the wire may be positioned within a non-conductive sleeve which also contains a gas chromatographic column, which is the thermal barrier between the wire and the gas chromatography column.

In another alternative approach, which is not part of the present Invention is the column coated directly with conductive metal, which is then resisted is heated to the column to heat. This eliminates the air gap (and the resulting delay in heat transfer) between the heated metal and the column. gas chromatography columns were previously coated directly with metal, especially aluminum, for the useful Temperature range of the columns to expand. Although these approaches been tracked to resist heating aluminum-lined capillary columns, are these approaches failed because aluminum tends to oxidize and there the thickness the aluminum coating is not sufficiently even over the Length of Pillar was. Both of these conditions resulted to "hot spots" and a non-uniform heating of Pillar. The uniformity the metal layer thickness can be increased by applying the metal layer directly to the molten silica the column. Oxidation can be avoided by coating the aluminum with a layer of polymer.

Heating and cooling of the gas chromatography column

Of the key to a high-speed gas chromatography is very fast Heating and cooling the column. For this purpose, the thermal mass of the column and the thermal mass, which is heated together with the column must be as small as possible being held. additionally to the electric heating technology discussed above can also used other techniques for heating the gas chromatography columns become.

heating technologies

A Technique uses infrared radiation to heat the gas chromatography column. In this technique, the column becomes coated with a material having a wavelength of absorbed by infrared energy emitted by an infrared source becomes. Energy from the infrared source is focused on the column so that the pillar the energy is absorbed and heated up by the absorbed energy becomes. An advantage of this technique is that a radiant heat transfer occurs almost immediately (i.e., at the speed of light) and that the only time delay, which is associated with this technique, from heating the glass or quartz tubing of the gas chromatographic column would result as soon as the energy passes through the coating material has been absorbed.

A another technique uses microwave energy to heat the column. The pillar is coated with a material containing microwave energy absorbed, and then rapidly by exposure to microwaves heated by a microwave source. For example, a thin metal film may be on the outside be placed in the glass or quartz tubing of the column. This Metal film absorbs the microwave energy to heat the column. One cooling down is achieved by blowing air over the surface of the Pillar.

Radio frequencies, how they are used to heat metal for welding, can used to the pillar to heat. A helix is placed around the pillar and high frequency spark energy is applied to the helix. This technique is extremely fast and does not require a big one thermal mass. A cooling is achieved by blowing air over the surface of the Pillar.

A additional Heating technology is to fire electrons on the surface of the column so that the Impact of the electrons causes rapid heating. This technique would be particularly suitable be with pillars shorter Length.

One Laser heating can be achieved by using the Quartz tube of the Pillar as a light path along which infrared energy from a laser transmits becomes. Coatings within the column become immediate and rapidly heated due to the absorption of some of the laser energy.

Heat of combustion can be used using natural gas or propane fuels, to achieve a rapid heating. The column can be replaced by applying a Flame directly at the column be heated or by providing the column with a catalytic Surface. For example, the outside can the column be coated with a catalytic material, so that a gas or another reactive compound which flows over the catalytic surface, absorbed becomes and is decomposed to heat which transmit to the column becomes. The pillar is cooled by Turning off the flow of gas and passing air over the surface the column.

One High pressure steam can be used to rapidly transfer heat to the column. These Technique uses concentric tubes in which the outer tube has a Contains high pressure steam and the inner tube the pillar contains (or is). This technique would a separate heater and a pressure system plus the piping require which needed are to lead the steam.

cooling techniques

In addition to Heating the column during one Analysis cycle, the system must be able to put the column on a desired one To cool equilibrium temperature, before the analysis cycle is initialized. The length of time which is necessary to this cooling which are referred to as the recovery time can, should be short, to provide a large sample throughput. In addition is it is often desirable to have a reproducible starting temperature. If the cooling technology fast enough, it may be sufficient to cool the column, possibly below the desired temperature, and then the temperature to the desired starting temperature exactly before initializing the analysis cycle.

The Lack of effective cooling technology has been a hindrance to a real high-speed gas chromatography to reach. In particular, you can high-speed gas chromatography systems require results repeatedly in less than 5 to 30 seconds to get. Because the Temperature of the column between successive analyzes must be reduced cooling mechanisms to be able to use the pillar to cool in much less than the analysis repetition time. To the Example must be after a temperature programmed or expiration High-temperature chromatogram, the gas chromatography column to her original, low (usually ambient) Return temperature, before the next Sample can be analyzed. Before this temperature reduction achieved by blowing ambient air or cooled air or other gas (such as carrier gas) over the gas chromatography column using a fan or blower. However, such fans have and blowers usually an inertia on which causes them for idle for a few seconds after being turned off. This has a few seconds delay before analyzing the next one Tested. If sample rates of the order of magnitude of several samples per minute are desired, this delay can be the Rate at which the samples can be processed significantly reduce.

Several Techniques have been used to control the gas chromatographic columns sufficient rates to cool. General close these techniques either blow relatively cold air over the air Column or thermal coupling of the column to another element, which is either cold to start, or which is very cooled quickly can be.

One technique uses liquid nitrogen as a cooling mechanism. Liquid nitrogen is German colder than ambient air, which leads to a very large temperature difference and extremely rapid cooling. Liquid nitrogen can be used by blowing the very cold nitrogen, vaporizing the liquid over the column to be cooled, and using simple flaps to turn the flow of cold nitrogen on or off. Liquid nitrogen can also be used by pumping the liquid nitrogen through a cold block similar to the aluminum block above 9 was discussed. When using liquid nitrogen, care must be taken to prevent water condensation from interfering with the operation of the system.

A other technique refers to adiabatic cooling, which is the cooling of a Gas is, which results from an expansion of the gas. adiabatic Cool Can be achieved by using a gas cylinder or a compressor and compressed air and compressed gas is allowed to expand in a controlled manner.

As above with respect to 9 discussed, Peltier coolers can be used to cool the gas chromatography column. A thin coating of insulating material may be used to prevent a thermal "short circuit" between the column and the aluminum block or other thermal mass cooled by the Peltier coolers Recovery time and the power required to heat the column Reducing the thickness of the insulation reduces recovery time, but increases the power that must be applied to the column to overcome the heat loss to the aluminum block when the column In general, the applicability of using Peltier coolers increases when the column is a short column, as used in a vapor concentrator, since a short column can be easily mounted in a cold block, which is protected by a Peltier Although gas chromatography columns used for sample analysis are also cooled H could be cooled by mounting them in a cold block, a more complex cold block would be required as these columns are typically longer and wound in a coiled fashion.

A Technology for using Peltier coolers to cool a gas chromatographic column is to use radiation fins in an insulated oven, which the gas chromatography column contains. These ribs are then cooled using Peltier coolers. If a cooling the column required is, becomes a circulating fan activated to the column exposed to the air, which is cooled by the Peltier cooler. The circulating fan will turn off when the pillar is heated.

The cooling rate for one The given analysis can be determined based on the cooling capacity of the cooling block (i.e., the cooling capacity of the Peltier coolers) and the temperature difference between the cooling block and to be cooled Pillar. As a result, the number of samples that are in a given amount can be analyzed in time, directly proportional to the cooling capacity of the Peltier cooler. Similar Results can can be achieved using a standard refrigeration system with a freon-type refrigerant. However, Peltier coolers are easier and tends to be more reliable. These types of cooling systems are most effective when the column or a vapor concentrator to a temperature below the ambient temperature chilled Need to become.

Also Water can be used as a refrigerant can be used, and it can be combined with antifreeze, if a chill below the freezing temperature of the water is desired. For example, water can or an antifreeze solution chilled be using a cooling system and then through or around the one to be cooled Components are pumped.

If ambient temperatures or temperatures are desired slightly above ambient, air convection can be used to cool the column. For example, an air convection technique will be discussed above with reference to FIG 1 discussed. In another technique, direct air cooling of the column or vapor concentrator can be replaced by air cooling of fins attached to a large cold block made of aluminum or other material.

Temperature measurement and control

Regardless of the techniques used to heat or cool the gas chromatographic column, the system must be able to accurately and accurately measure and control the temperature of the gas chromatography column for efficient, high-speed analysis of the samples. As in U.S. Patent No. 5,268,302 As disclosed, the gas chromatographic column may require to be at different temperatures during different portions of the analysis. For example, a representative profile of a desired temperature change over time is 17 shown.

The temperature of the gas chromatographic column can be varied by controlling the electrical current applied to the resistive tube the column is created. In previous gas chromatography systems, exemplified by U.S. Patent No. 5,108,705 and 5,300,758 As shown, temperature programming has been achieved by proportional control of the voltage applied to the column. An increase in applied voltage resulted in an increase in the current flowing through the metal sleeve of the column and a corresponding increase in the temperature of the column. When full power was not required (as when the column was maintained at a temperature plateau), power was dissipated by a control transistor. Settings in the system had to be changed from time to time to compensate for any changes in the resistance of the sleeve, such as installing a different gas chromatographic column for a different analysis, where an exchange column differed in length, wall thickness or diameter due to manufacturing variations.

Referring to 18 For example, the present approach uses a processor 800 to continuously test the resistance of the gas chromatography column. The resistance of the metal sleeve is a function of its temperature and can be expressed, for example, by: R = R 0 (1 + K (T - T 0 )), where R is the resistance at a temperature T, R _{0 is} the fixed base resistance (eg at ambient or base temperature T ₀ ) and K is the temperature coefficient of resistance of the sleeve material which is a known constant value for the particular material. It follows that a temperature (T) is a linear function of the resistance (R), which can be expressed by: T = T 0 + K '(R - R 0 ) where K 'is also a constant. Therefore, the change in temperature from a base or ambient value (ie, T - T ₀ ) is a linear function of the change in resistance (ie, R - R ₀ ). Accordingly, the resistance of the column can be taken as a representation of the column temperature once the resistance of the column at a base or ambient temperature is determined.

The profile of 17 shows the desired temperature at each instant during the gas chromatographic analysis period. The microprocessor 800 Simply determine the current time during the analysis period by counting the clock pulses or cycles of the clock oscillator of the microprocessor from the beginning of the analysis period. Since the desired temperature at each instant along the profile is known, the desired resistance at each instant can be determined using the desired temperature, known start resistance and temperature, and resistivity coefficient. The resistance values may be stored by the microprocessor in a data table, or they may be processed, if necessary, by interpolation between the known slope change points of the temperature profile.

The functions of the system and its software are shown in the flowchart of 19 shown. Initially, the user defines a desired profile of the temperature over time and passes the profile to the processor 800 to (step 900 ), either in the form of a table or as a fixation of the temperature change. For example, a typical temperature profile for a vapor concentrator may raise the temperature from a starting or ambient value of 250 ° C as quickly as possible and then maintain that temperature for two seconds. For the gas chromatography column may be a typical temperature profile, as in 17 in which the temperature is raised from the starting temperature to 100 ° C in ten seconds, maintained at 100 ° C for ten seconds, raised from 100 ° C to 200 ° C in the next ten seconds, at 200 ° C for is maintained for the next twenty seconds and then returned to the starting temperature as quickly as possible.

The processor 800 stores or converts the user supplied data for a desired temperature over time into a table of desired resistance over time (step 905 ) around. Where a resistance changes uniformly with time, the value at different temporal moments can be calculated by interpolation instead of being stored as a table. The processor generates this data using the base column resistance at a known temperature and the temperature coefficient of resistivity for the column. The processor determines the base resistance by measuring the column resistance during the passage of air having a known temperature measured across the column.

The processor controls the temperature in successive control intervals or cycles. The processor initializes the gas chromatographic temperature profile upon injection of the sample into the gas chromatography column from the vapor concentrator, as discussed above (step 910 ), and counts down clock pulses to determine the subsequent control intervals. Each control interval can be from about 1-10 milliseconds in duration. At each control interval, the processor measures the column resistance and, if necessary, adjusts the column temperature. In particular, the processor applies a reference current to the sleeve (step 915 ) to the Wi the resistance of the sleeve to measure (step 920 ), and then compares the resistance to the stored table value for that control interval (step 925 ).

If the measured resistance is less than the desired value (step 930 ), the processor applies a voltage to the sleeve (step 935 ). Otherwise, the processor will not apply voltage to the sleeve. The system then repeats the cycle during the next control interval by repeating the step of applying a reference current to the sleeve (step 915 ) and the steps that follow.

As in the timing diagram of the 20 shown, each control interval has three successive stages: a measuring stage I, a heating stage II and a waiting stage III. During measurement stage I, the processor measures the actual sheath resistance by applying a small voltage to the metal sheath and compares the actual resistance to the desired resistance. If the measured resistance is below the desired resistance, this indicates that the column temperature is below the desired (profile) temperature. The processor responds to this condition by applying a heating voltage to the metal shell during heating stage II. This voltage may be of fixed duration which is less than or equal to the control interval.

The Duration of heating level and control interval are selected based on the heat capacity of the gas chromatography column and the desired Accuracy of temperature control. Illustrativ may, if one Temperature control accuracy of 0.1 ° C is desired, then the temperature the gas chromatography column not more than 0.1 ° C in any single control cycle, since the temperature measurements be performed only once in each control cycle. Thus, in this Example, if the heating voltage is capable of the temperature the gas chromatography column at a maximum rate of 20 ° C per second, then the duration of the heating power to one fixed duration of 5 milliseconds or less. During the remaining time of the control interval no voltage is applied to the column. Accordingly, this will Stage of the control interval referred to as a waiting stage III.

For a typical, six meters long gas chromatography column is the resistance at Ambient temperature at about 12.8 ohms. A heating voltage of 90 Volt becomes a temperature increase of over 10 ° C per second produce. Accordingly, a Applying the heating voltage of 90 volts for a millisecond a temperature increase of approximately 0.01 ° C cause. In the case of the steam concentrator is a typical starting resistance 0.50 ohms, and a heating voltage of 24 volts will cause a temperature increase of 4 ° C in one millisecond.

By using a short control interval, the processor is 800 capable of controlling the temperature of the gas chromatographic column or vapor concentrator in accordance with the desired profile. Since the control intervals occur very rapidly, each for a period of one to a few milliseconds, the effect is to reach the desired temperature very quickly and maintain the temperature substantially at the desired value until a change is required.

As in 18 shown closes the gas chromatography column 805 electrical connections 810 and 815 at the ends of the metal sleeve of the column so that a voltage applied across the terminals creates an electrical current in the sleeve which heats the column to the desired temperature. The connection 810 is with a first connection of a circuit breaker 820 connected by the processor 800 is controlled. In a first position, the switch connects 820 a power source 825 between the connections 810 and 815 , The power source 825 generates a small measuring current of eg 100 mA. In a second position, the switch connects 820 a fixed voltage source 830 between the connections 810 and 815 , The voltage source 830 generates a large voltage (eg about 90 volts for the column 805 or 24 volts for a vapor concentrator) which serves to heat the column. In a third position, the switch is open so that no voltage is applied to the column.

An analog-to-digital converter (ADC) 835 measures the voltage between the terminals 810 and 815 and provides a digital signal indicative of the voltage to the processor 800 , If the standard current (eg 100 milliamps) is applied to the sleeve, the through the ADC 835 Voltage designated the resistance of the sleeve again. For example, if the ADC indicates one volt for a 100 milliampere current, the resistance would be 10 ohms. This voltage is applied to the processor in digital form. As pointed out above, this voltage represents the measured sleeve resistance at each control interval.

The processor compares the resistance value provided by the ADC 835 , with the corresponding desired resistance. If the desired resistance is determined to be higher than the measured resistance, indicating that the column temperature is lower than desired, the processor controls the switch to turn off the high voltage source 830 to the pillar for a vorbe agreed fixed time to connect. This provides additional heating energy to the load to increase its temperature and thus its resistance. At the end of this period, the processor changes the switch to the open position (III) for the time spent in the control interval. In the next control interval, the processor reconnects the standard power source to the load and measures the resistance. If the resistance and the temperature are below the desired values, then the processor connects the voltage source 830 with the pillar. These cycles are repeated at a high rate (eg, about once every one to ten milliseconds) until the processor determines that the measured resistance is at least equal to the desired resistance. If this condition exists, the processor places the switch 820 in the open position (III) for this control interval. This pattern of measurement, followed by waiting, continues until the measurement in a control interval indicates that the temperature needs to be increased. At this time, processor connects 800 again the voltage source 830 with the column for a fixed period of time.

The control scheme can be further refined to allow finer control of the temperature. The procedure of 19 uses on / off temperature control (ie during the power period the heating power is either fully on for a fixed period of time or off completely). Finer control can be achieved by proportional control or by more sophisticated control schemes known as proportional integral (PI) or proportional integral derivative (PID) control.

In these techniques, the heating power is varied according to the size of the error signal, ie the difference between the actual temperature and the desired temperature. This can be achieved by varying either the heating voltage, as in the U.S. Patent No. 5,300,758 or by varying the duration of the power period. Processor-based devices that implement PID through such time proportionality are well known in process control. One example is the CN4400 omega model available from Omega Engineering of Stamford, Connecticut. Algorithms for PID control are described in Perry's Chemical Engineer's Handbook, Sixth Edition, pages 22-77, McGraw-Hill, New York 1984, in, for example, equations 22-30 at pages 22-77.

As in 21 4, the duration of the heating period may be controlled based on the relationship between the measured resistance (R _m ) and the desired resistance (R _d ) to achieve time-proportional PID control. Using the PID algorithm, the computer calculates the required voltage duration during each control interval. The circuit of 18 works as discussed above, except that the processor 800 the voltage source 830 disconnects after the heating stage has had a desired period of time, rather than after a fixed period as described above. This offers a pulse duration variation analogous to pulse width modulation (PWM).

In this way, the temperature of the column is repeatedly measured and the power is supplied to the system as necessary to closely follow the desired temperature profile, as in 17 shown until the profile calls for a rapid decrease in temperature, as at the end of the analysis cycle.

The approach described above allows one column to be easily replaced by another without requiring recalibration and automatically accounts for any difference in column column resistance that the replacement column may have. If a measurement at base (eg, ambient) conditions for the replaced column determines that R ₀ has changed for the base temperature, the processor recalculates each of the resistance values stored in its memory to a new modified resistance table for the system to deduce to follow for the replaced column. This can be easily achieved because each R value in the stored table should be adjusted by the same amount in response to a change in R ₀ to keep the same profile.

By this arrangement is no longer necessary the system indicates replacement of a column with a new column, which a different length or base resistance may recalibrate. The basic resistance the replacement pillar is determined automatically, and the table of the desired Resistance at each control interval instant will be for the new ones stored column resistance values recalculated by reducing each resistance value by the difference between the previous and the new base resistances, without to require a different recalibration.

the desired Temperature profile is then for the new pillar while the control intervals closely followed, as described above. Thus, can the pillar be structured as an easily replaceable module, if desired, without manual recalibration is required after replacement close.

The gas chromatography column may require heating to different temperatures to move quickly from one temperature to another. Temperature control may require it to be highly accurate over wide temperature ranges.

As discussed above, is a technique for measuring the temperature of Gas chromatography column, measure the electrical resistance of a metal sleeve surrounding the column, when the power used to heat the column is not applied is. A known relationship between resistance and temperature can be a temperature measurement with an accuracy of the order of magnitude of 0.5 ° C and an absolute accuracy of ± 2 ° C over a wide temperature range from 25 ° C up to 400 ° C allow. This resistance measurement technique can work well if a control cycle is divided into a measuring section, in which the temperature is measured, and a heating section in which through the metal sleeve Applying an electric current is heated. A MOSFET transistor or a similar control Can be used so that a heating energy is not during the Measuring section of the cycle is consumed. This procedure facilitates the Design of economic, compact and simple systems for controlling, measuring and rapidly changing the Temperature of a gas chromatography column or a vapor concentrator.

Other Techniques can also used to change the tube temperature to eat. For example, the temperature can be measured below Use of a radiation pyrometer or a distributed thermocouple. A distributed thermocouple uses coaxial wires, which are made of different metal len and which surround the gas chromatography column. Different combinations of materials in the distributed Temperature sensors can more sensitive and accurate sensors for specific temperature ranges Offer. Pyrometers provide electrical and thermal insulation.

techniques for providing a controlled heating of the column include the application of width modulated Pulses of energy to the column and an ON / OFF control of the application of heating energy with short Temperature measuring intervals, enabling up to 98% working cycles. A quick switch between a measurement and a controller allows It allows the system to achieve a high-precision temperature profile Reducing the duration of the control cycle, which is as short as 100 microseconds can be.

An arrangement for heating and cooling a gas chromatography column 1000 is in the 22 and 23 shown. As previously noted, the column may be an internally coated quartz capillary tube screwed into the inside of a very small (eg, 0.02 inch diameter) metal needle tube, as described in more detail in U.S. Patent Nos. 5,496,055 U.S. Patent No. 5,300,758 in column 5, lines 44-66.

The pillar 520 is coiled in a helix or helix and within an annular housing 1005 placed, which has a cylindrical outer wall 1010 and a cylindrical inner wall 1015 which together form an annular space 1020 define. The coiled column 1000 has an inlet 1025 and an outlet 1030 on. The upper end of the annular housing 1005 is to an outlet port 1035 coupled. Air from a centrifugal fan 1040 or another similar source becomes an inlet port 1045 fed to cooling air in the annular space 1020 to push which is the pillar 1000 contains. Air can also pass through an internal passageway 1050 pass through, defined by the inner wall 1015 , An annular cover or damper 1055 covers the inlet of the annular space 1020 and is by a magnet 1060 controlled. In the absence of excitation of the magnet becomes the damper 1055 held in an open position, either under the influence of gravity or by a suitable spring. On a sub-energy setting of the magnet 1060 The damper closes 1055 and prevents air from flowing into the annular space 1020 whereas it has little, if any, effect on air, which within the internal passage 1050 flows.

The damper 1055 is kept closed during the part of the operating cycle of the gas chromatography system in which the column 1000 is heated and the chromatograph is generated. At the end of this portion of the cycle of operation, the column is rapidly cooled by turning off the mechanism (eg, electric current) used to heat the column and opening the damper to provide cooling air through the annular space 1020 to allow. The resulting forced air convection leads the column 1000 quickly returned to the original cold state of the column. An air stream for cooling the gas chromatography column 1000 enters through an inlet at the back of the gas chromatography system, passes through the connection system under the influence of the centrifugal blower 1040 through and is returned to an outlet on the back of the instrument.

A similar arrangement can be used to determine the temperature of a vapor concentrator 515 (or more steam concentrators) to control. The concentrator may be enclosed in its own housing, with depressed air provided for cooling. A damper can be used to abruptly cut off an airflow as soon as a desired low temperature is reached. The damper is controlled as described above.

In In some arrangements, a common housing for the gas chromatography column and the Concentrator or concentrators are used, so that one single fan and damper control assembly this serves both the gas chromatography column and the concentrator to cool. If a single blower is used individual dampers for every Device be provided so that the devices independently too Chilled at different times can be, where Some devices are heated while others are cooled. Alternatively you can individual housing and dampers used to air for to control the individual concentrators.

For some applications, such as detecting permanent gases and light hydrocarbons, it is desirable to use the gas chromatographic column 1000 operate at temperatures as low as 15 ° C and the steam concentrator at temperatures as low as -10 ° C. For these applications, the air, which leads to the annular space 1020 is provided to pass through a cooled heat exchanger (not shown) to cool the air to temperatures below ambient. Use of a cooled heat exchanger or similar device may be particularly important in industrial process control applications where the ambient temperature may be as high as 40 ° C.

temperature gradients

The annular geometry facilitates rapid cooling. This geometry is also relatively compact, which is an advantage for the package design of an instrument that supports the column 1000 contains. However, as in 24 As shown, undesirable temperature gradients may result from this geometry. In particular, the two helical coils tend 1100 on the ground to be much colder than the other coils 1105 the column 1000 , This has been experimentally observed both by using thermocouples and by inspecting the gas chromatographic column for darkening due to the exposure to heat.

The temperature gradient occurs due to convective air flows, which lead to a so-called chimney effect. This is an asymmetry between the lowest turns of the helix 1100 and all subsequent turns. Air, which is heated by the lowest helices of the helix, rises and creates a warmer environment for the spirals immediately above. As the heated air rises, the heated air loses heat to the walls of the chamber in which the column is 1000 is included. This can lead to a steady state condition in which the local temperature is independent of the vertical position, except for the lowest helix turns, which are not heated from below.

It should be noted that the two lowest coils 1100 rather than just the single lowest coil being different from the other coils. A simple explanation for this is that the vertical distance required to reach a steady state temperature as a result of cooling by the annular walls is greater than the vertical height of one turn of the helix.

25 shows an alternative configuration in which a short trap column 1110 is mounted immediately below the analysis gas chromatography column. The trap column 1110 includes a metal capillary identical to that of the column 1000 , and it has a coiled geometry and a spacing identical to that of the column 1000 but it is not with the gas flow of the column 1000 connected. The trap column 1110 acts like the lowest coils 1100 the helix indicates the presence of an undesired thermal gradient in the column 1000 to prevent. Electric are temperature sensing cables 1115 and 1120 over the pillar 1000 attached while the electric heating current in series both through the column 1000 as well as the trap column 1100 from a first cable 1125 to a second cable 1130 flows.

26 FIG. 4 illustrates an alternative gradient prevention technique in which several features are compared to the configuration of the FIG 22 have been added. First is the inner wall 1015 about 0.25 "at the top and 0.25" at the bottom have been shortened to the airspaces 1020 and 1050 Both at the top and at the bottom zwischenzuverbinden. Second is a damper mechanism 1200 at the top of the case 1005 so added that the airspace of the housing 1005 can be isolated from the headspace of the outlet connection during gas chromatographic analysis. The third is a fan or blower 1205 installed a flow of air in the closed ring between the rooms 1020 and 1050 to create. The speed of the air flow is selected by controlling the voltage to the drive motor 1210 of the fan, and the direction of the air flow is selected by the choice of fan type of the fan 1205 and the placement of the fan 1205 inside the case 605 , For example, fans having centrifugal propellers may be at the top or bottom of the housing ses, whereas an axial fan in the middle of the room 1050 can be placed. The airflow in the closed ring mixes the air and eliminates or reduces the vertical thermal gradient.

One Another problem with vertical thermal gradients in the Context, is that due to temperature differences, which result from the thermal gradient, the upper coils one higher Have resistance as the lower coils and consequently with a higher one Heat rate as the rate at which the lower coils heat.

The Using a fan, as discussed above, eliminated or reduces the vertical thermal gradient by bringing the Pillar to that it is thermally homogeneous. Another technique to the thermal Eliminating or reducing gradients is the entire process Insulate the length of the column.

One Way to isolate the length the column is it, the pillar over one huge Range to stretch and big distances between all parts of the column allow. This prevents thermal crosstalk between different ones Split the pillar. The problem with this technique is that it is remarkable Would require space and for that reason can be impractical.

One another way of isolating the length of the Pillar is it, the pillar to place in a vacuum. This would cause heat transfer due to convection eliminate. However, you can considerable Difficulties associated with sealing the system and a cooling according to the column every analysis.

One another way to the pillar It is the pillar that isolates it to place in a thermally insulating sheath. For example could the case made of glass fiber, a polymer similar to Teflon or any other coating material, which is a thermal insulation and which does not break as a result of the high temperatures, on which the pillar is heated. With an insulating sheath, each section of the column would be independent of the other section to be heated. Another advantage of this technique would one reduced heat loss and a consequent reduction in energy consumption. If a tubular insulation would be used instead of placing the column in a metal sleeve, could the pillar run parallel with a heating wire, placed in the insulating Tube. In general, that would the heating wire a higher Resistance than the metal sleeve, and for that reason it would be easier to be controlled. A problem with thermal insulation the column and the heating element is in a resulting Increase in the time required to cool the column. One other problem would to be an inability to reverse the deviation of the temperature of the column when the temperature as a ramp is led or starts up.

As noted above, the temperature of the column can be made homogeneous by using a fan to control the air in the inside of the room 1020 to mix. In this technique, the housing should 1005 be sealed and all surfaces should be insulated to minimize heat loss. Violent movement of air ensures that there are no temperature gradients and that the entire column starts at the same temperature and stays the same when the temperature starts up. A problem associated with this technique is that more power is required to heat the column because a relatively large volume of air must be heated together with the column.

In some cases Thermal gradients along the length of the gas chromatographic column are desirable. In particular, you can higher resolution gas chromatographic separations can be achieved by providing a changing temperature along the length the column. For example, a continuously changing temperature can begin at a high temperature at the injection end of the column and ending at a lower temperature at the detection end of the column while improving the resolution from certain samples. Techniques for achieving temperature changes along a gas chromatographic column are described below.

In a first technique, like in 27A pictured is a pillar 1300 vertically in a container 1305 suspended for liquid or gas heated from the top of the container. A soft thermal gradient is to be achieved, but this can be difficult to control. temperature sensors 1310 can be installed along the length of the column to measure the operating temperature at any point. Oil or air may be suitable working fluids for typical gas chromatographic temperatures.

In a second technique, like in 27B shown, serves a resistance-heated metal tube 1315 as a gas chromatographic column. The inner diam water 1320 the column is constant along the length of the column. The outer diameter of the column decreases at a constant rate from the inlet 1325 to the outlet 1330 too, resulting in a growing cross section, a waning counter and decreasing power dissipation along the length of the column from the inlet to the outlet. The column is mounted in a chamber in which a circulated fluid, such as air, removes heat from the column at a fairly uniform rate and is heated using a low voltage, high current power supply.

The Temperature profile can be tailored by adjusting the Rate at which the cross-sectional area changes along the column. To the Example would a linear change, which to a conical column leads, depending on a temperature profile of a root law. One desired Degree of change along the length can be achieved by controlling the change in the cross section along the length. The operating temperature at any point, but not the profile, can be changed are adjusted by adjusting the electrical current which is to Column is supplied.

In a third technique, like in 27C shown, becomes a coating 1335 with variable conductivity on a glass column 1340 applied. In particular, the coating is vaporized or coated on the column to achieve variable watt density along the length of the column. This technique offers a potential advantage over that in 27B As shown, it may be less expensive to produce a column having a variable resistance coating than to produce an accurate profile in a metal tube. Once again, it is believed that heat is transported away from the column at a fairly uniform rate to achieve the desired temperature profile.

In a fourth technique, as shown in 27D , becomes a metal or glass tube 1345 of constant cross-section, together with an external electrical heater, which produces a variable watt density along the length of the column. The variable electric heater can be manufactured, for example, by winding a wire 1350 around the column in a spiral, which has a slope that varies along the length of the column. A potential disadvantage of this technique is that the spiral temperature profile could be transferred to the inside of the column to form a series of hot and cold spots along the length of the column. Using current manufacturing techniques, a column wrapped with wire in a variable pitch spiral would be relatively expensive to manufacture. This is an important consideration as the column must be considered as a wear or disposable part.

In a fifth technique, as shown in 27E , heat is removed from a uniformly heated column at different rates along the length of the column. For example, annular cooling fins 1355 of variable diameter along the length of a metal tube 1360 be installed, which has a constant cross-section and is heated by an electrical resistance, and a fluid can be circulated around the tube to remove the heat from the tube. The amount of heat removed from different parts of the tube will vary with the size of the ribs attached to the different portions of the tube, which will result in a variable temperature profile along the length of the tube.

In a sixth technique, as shown in 27F , a thermal gradient is achieved along the column 1365 by adding heat to one end of the column using a heat source 1370 and removing heat from the other end of the column. This technique requires significant isolation of the column. For example, a metal column installed in a vacuum could achieve this effect. It would be difficult to build a column of the required length in this way without using a highly conductive metal.

flow control

A other important consideration is a flow control within the system. In a chromatographic system, the relative stability the flow of a carrier gas between analyzes a significant influence on whether the by the system generated results are reproducible. Accordingly, a must Gas chromatography system to be able to consistent the flow of carrier gas or to control evenly. About that In addition, some analyzes require changes in the flow of the carrier gas. For this Analyzes, the system must be capable of consistently variable rivers to build.

Flow control may be particularly important during temperature programming. As the density of the carrier gas changes as a function of temperature, the flow through a particular flow restrictor will continuously change with the changing temperatures associated with temperature programming. The system may add another dimension to the controller by providing the ability to control and vary the carrier gas flow. The flow can be controlled using a mass flow controller. A less expensive method is to use a series of flow restrictors, such as capillaries or similar devices, and a number of associated ones To use solenoid valves, which allow selective activation of different flow restrictors or combinations thereof, to vary the flow through the system.

Other Flow control points are also relevant. For example, as above mentioned, has been found to be a backwash of the steam concentrators (i.e., a reversal of the current through the steam condensers desorbing contaminants from the vapor concentrators) leads to a more rapid chromatography. The use of backwashed steam concentrators also allows the use of stacked steam concentrators (I.e.,

Dampfkonzentratoren, which are arranged in series) with a first Dampfkonzentrator, which for materials which is a relatively low volatility and the second vapor concentrator used for materials is optimized, which have a high volatility.

sound waves can be used to the currents through the system. If a sound transmitter, which at one end of a tube is positioned, a sound generated by a sound receiver at captured the other end of the tube will be, by the recipient received sound have the same frequency as the sound, which is generated by the transmitter, if no gas flow through the Tube is present. If there is a gas flow, then the received frequency from the transferred Frequency differ as a function of gas flow and other easy factors to be measured. This effect could be used to Gas flow to be measured within the gas chromatography column. Note that the frequency that is used has to be that the corresponding one wavelength is small compared to the diameter of the column.

The sample extractor

A Sample can be obtained by wiping surfaces believed to be that they contain sample material, or by blowing air such surfaces, to solve substances to be analyzed, and collecting a sample for an investigation of the object that was used to the surface to wipe off, or from the blowing air. However, such methods can not being appropriate for a sensitive study of granular or particulate materials, which wear or are coated with unwanted substances. For example the wiping technique may be unsuitable for the detection of pesticides on wheat grains or other crops.

28 shows a schematic, elevated cross-section of a sample extraction module 1400 which can be used as a sample extractor 510 the system of 15 , The sample extraction module 1400 provides an improvement over previous "free space analysis" and solvent extraction methods used to analyze granular or particulate materials In a free space analysis, a collected sample is placed in the bottom of a vessel and a stream of carrier gas is passed over the sample In contrast, the present method forces a heated carrier gas through a bed of granular, solid material so that the heated gas is in intimate contact with the various gases from the solid sample and into the carrier gas stream Surface of the granular material is placed, and extraction of volatile components and removal of adhering substances is both fast and reproducible, resulting in a typical sample extraction time ranging from 10 seconds to a few minutes, depending on the nature of the In contrast, clearance techniques typically require one hour or more for sample collection.

Similarly required earlier Solvent extraction techniques typically several hours to get a sample and they also required an expensive disposal of waste solvents. The extractor of the present invention is particularly adapted contaminants, such as pesticides, which are granular products, like wheat grains or other crops or granular materials, with one layer surrounded, extract.

The extractor module includes a funnel-shaped housing 1405 with dimensions appropriate to the size of the desired sample. The housing 1405 is capable of about through a cover 1410 to be sealed, and it has an inlet 1415 to pick up carrier gas. The granular material 1420 which is to be analyzed will be inside the funnel 1405 on a screen or filter 1425 placed. A diffuser 1430 can be at the top of the material 1420 be placed to distribute the carrier gas. The exit 1435 from the funnel 1405 enters the wall 1440 a furnace containing valves and other components of the gas chromatography system.

The funnel 1405 and the cover 1410 are heated electrically to between 100 ° C and 300 ° C. After adding a granular material 1420 and sealing the cover 1410 against the body of the funnel 1405 is a heated carrier gas or air (at a temperature of about 150 ° C-300 ° C) through the granular material and into the oven.

Volatile components which are layered on or contained in the sample material 1420 are released from the sample material and enter the carrier gas stream which is fed into the system for processing and analysis.

The detector

In a conventional one Gas chromatography system, the volume of the detector plays an important Role in determining the sensitivity and resolution of Analysis. Standard detectors can Detect gas chromatographic peaks which are about 0.5 second wide or are wider. However, high-speed gas chromatography systems, such as the system of the invention, peaks less than 0.1 Seconds are wide. If two adjacent peaks, each of which is 0.1 Seconds wide and which are separated by 0.2 seconds (resolution = 2), by a conventional Detector would be detected, would the peaks both occupy the detector cell at the same time, and the resolution would be impaired.

The effective volume of a detector can be reduced (and the resolution can be increased by operating the detector under vacuum. For example, when a flame ionization detector is operated under vacuum, the hydrogen flame will lengthen, and the chemistry of ionization, which occurs at different flame temperatures can be distinguished by using multiple collectors. Answers, which for functional Groups of the analyte are specific, can be used to a selectivity and To improve the sensitivity of the analysis.

Claims (20)

A high-speed gas chromatography system, comprising: a detector; a heated isothermal area; a conductive metal sleeve ( 165 ); a gas chromatographic column ( 150 ), whereby the column ( 150 ) within and separate from the sleeve ( 165 ), wherein an outer diameter of the column ( 150 ) is smaller than an inner diameter of the sleeve ( 165 ), so that the difference between the two diameters is small enough to allow rapid heat transfer from the sleeve (FIG. 165 ) to the column ( 150 ) and the column ( 150 ) and the sleeve ( 165 ) are located external to the isothermal region; and a flow path between the detector and the gas chromatographic column ( 150 ), wherein at least a portion of the flow path is positioned in the isothermal region. The system of claim 1, further comprising a housing ( 110 ), external to the isothermal region, wherein the gas chromatographic column ( 150 ) in the housing ( 110 ) is positioned. A system according to claim 2, wherein the housing ( 110 ) to the gas chromatographic column ( 150 ) of heat sources outside the housing ( 110 ) to isolate. The system of claim 3, further comprising a circuit for supplying an electric current to the conductive metal shell ( 165 ), for heating the gas chromatographic column ( 150 ). The system of claim 3, further comprising an insulating wall between the housing ( 110 ) and the isothermal area. A system according to claim 2, wherein the housing ( 110 ) includes an inner surface having a low thermal mass. The system of claim 2, further comprising a blower positioned in the housing (10). 110 ) to a substantially homogeneous heat distribution within the housing ( 110 ). The system of claim 2, further comprising: an inlet configured to operate in an open position that injects power into the housing (10); 110 ) through the inlet, or a closed position, which allows a flow into the housing ( 110 ) through the inlet and a control mechanism mounted on the inlet and operable to switch the inlet between the open and closed positions. The system of claim 8, further comprising a processor configured to control the system, wherein the processor is connected to the control mechanism and configured to cause the control mechanism to set the inlet to an open position to open the chromatography column. 150 ) to cool. The system of claim 1, wherein the heated isothermal Area has a heated isothermal chamber. The system of claim 1, further comprising a circuit for supplying an electric current to the conductive metal shell ( 165 ), for heating the gas chromatographic column ( 150 ). A system according to claim 11, wherein the gas chromatographic column ( 150 ) further comprising a layer of electrically insulating material, which the conductive metal sleeve ( 165 ) surrounds. A system according to claim 1, wherein the gas chromatographic column ( 150 ) with the sleeve ( 165 ) is arranged in a coiled configuration. The system of claim 13, further comprising a holder configured to support the column (10). 150 ) with the sleeve ( 165 ) in the coiled configuration. The system of claim 14, wherein the holder has four side rails and a pair of rings, with the side rails connected with the rings. The system of claim 15, wherein each of the side rails includes grooves on a surface of the side rails that lies within the holder, each groove sized, a helix of the column ( 150 ) with the sleeve ( 165 ). A system according to claim 1, wherein a heat sink at each end of the sleeve ( 165 ) is attached. The system of claim 17, wherein the isothermal region comprises an isothermal chamber, the system further comprising a retainer positioned in an outer wall of the isothermal chamber, a first heat sink attached to a first end of the sleeve. 165 ) is configured to be inserted in the holder. The system of claim 18, further comprising a second support positioned in the outer wall of the isothermal chamber, a second heat sink attached to a second end of the sleeve (10). 165 ) is configured to be inserted in the second holder. The system of claim 19, wherein: the heat sinks attached to the ends of the metal shell ( 165 ), are electrically conductive; and the brackets are configured to provide an electrical current for heating the column by attaching the brackets to the heatsink.